Field
The present disclosure relates to the design of an optical source. More specifically, the present disclosure relates to the design of an optical source that includes ring-resonator modulators within an optical cavity.
Related Art
Silicon photonics is a promising technology that can provide large communication bandwidth, low latency and low power consumption for inter-chip and intra-chip connections or optical links. A key component for a silicon-photonic optical link is an efficient high-speed optical modulator, which is used to convert a high-speed electrical data signal into an optical signal. For example, optical modulators are often used with continuous-wave optical sources, such as lasers. The requirements for an optical modulator are: high speed, low power consumption, low optical loss, a high ON/OFF extinction ratio (ER), and compact size.
Most of the existing high-speed optical modulators in silicon photonics are based on the free-carrier plasma dispersion effect: the index of refraction of silicon decreases as the densities of electrons and holes (i.e., free carriers) increase. In order to use the free-carrier plasma dispersion effect for data modulation, the carrier densities in an optical waveguide are typically electrically modulated. In turn, this modulation modulates the index of refraction and, thus, the optical phase of the propagating laser light. The phase modulation can then be converted into optical intensity modulation (i.e., ON/OFF switching) using a ring-resonator modulator or a Mach-Zehnder interferometer (MZI).
Ring-resonator modulators use strong resonances for modulation, and thus can achieve large ER even with a weak phase modulation. However, ring-resonator modulators typically require precise and dynamic tuning to align the resonance with the laser wavelength. This precise and dynamic tuning can be difficult to implement, and often consumes a large amount of electrical power and results in control circuits that occupy large areas on integrated circuits. While MZI modulators do not need precise and dynamic tuning, they typically need much stronger phase modulation in order to achieve a large ER. Therefore, MZI modulators are usually very long, and need high modulation voltage/power.
Hence, what is needed is a technique for modulating an optical signal without the above-described problems.